• We describe six Italian families afby microcephaly with an apparently autosomal mode of inheritance (total number of microcephalic children and adults, 21). All microcephalic subjects were of normal height, with the exception of one. The head volume was measured directly in at least one adult microcephalic member from five of the six families, and lower values were obtained in these subjects than in control subjects. Psychometric tests were performed on seven children and five adults among the microcephalic subjects. Normal values were found for all but one of the subjects. In the selected families microcephaly seems to be inherited in an autosomal dominant manner. Because some families showing autosomal dominant microcephaly have normal intelligence, psychometric evaluation of microcephalic children and their microcephalic relatives is important for genetic counseling.